From 549389d3274f9148d5aab5f30133a03289af76db Mon Sep 17 00:00:00 2001
From: Moonchild <moonchild@palemoon.org>
Date: Wed, 18 Jan 2023 14:08:50 +0100
Subject: [PATCH] No issue - factor out some frame iterator helper functions.

---
 js/src/jit/JitFrameIterator-inl.h |  6 ++++++
 js/src/jit/JitFrameIterator.h     |  4 ++++
 js/src/jsopcode.cpp               | 12 ++++++------
 js/src/vm/Stack.cpp               | 15 +++++++++++++++
 js/src/vm/Stack.h                 |  3 +++
 5 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/js/src/jit/JitFrameIterator-inl.h b/js/src/jit/JitFrameIterator-inl.h
index 6854941c37..c13e1670b2 100644
--- a/js/src/jit/JitFrameIterator-inl.h
+++ b/js/src/jit/JitFrameIterator-inl.h
@@ -35,6 +35,12 @@ JitFrameIterator::baselineFrame() const
     return (BaselineFrame*)(fp() - BaselineFrame::FramePointerOffset - BaselineFrame::Size());
 }
 
+inline uint32_t
+JitFrameIterator::baselineFrameNumValueSlots() const {
+    MOZ_ASSERT(isBaselineJS());
+    return baselineFrame()->numValueSlots();
+}
+
 template <typename T>
 bool
 JitFrameIterator::isExitFrameLayout() const
diff --git a/js/src/jit/JitFrameIterator.h b/js/src/jit/JitFrameIterator.h
index 417d11afcc..b5b217b4e1 100644
--- a/js/src/jit/JitFrameIterator.h
+++ b/js/src/jit/JitFrameIterator.h
@@ -256,6 +256,10 @@ class JitFrameIterator
 
     inline BaselineFrame* baselineFrame() const;
 
+    // Returns the number of local and expression stack Values for the current
+    // Baseline frame.
+    inline uint32_t baselineFrameNumValueSlots() const;
+
     // This function isn't used, but we keep it here (debug-only) because it is
     // helpful when chasing issues with the jitcode map.
 #ifdef DEBUG
diff --git a/js/src/jsopcode.cpp b/js/src/jsopcode.cpp
index 30fcd0c87a..1ba19731eb 100644
--- a/js/src/jsopcode.cpp
+++ b/js/src/jsopcode.cpp
@@ -1568,18 +1568,18 @@ DecompileExpressionFromStack(JSContext* cx, int spindex, int skipStackHits, Hand
 
     FrameIter frameIter(cx);
 
-    if (frameIter.done() || !frameIter.hasScript() || frameIter.compartment() != cx->compartment())
-        return true;
+    if (frameIter.done() ||
+        !frameIter.hasScript() ||
+        frameIter.compartment() != cx->compartment() ||
+        frameIter.inPrologue()) {
+      return true;
+    }
 
     RootedScript script(cx, frameIter.script());
     jsbytecode* valuepc = frameIter.pc();
 
     MOZ_ASSERT(script->containsPC(valuepc));
 
-    // Give up if in prologue.
-    if (valuepc < script->main())
-        return true;
-
     if (!FindStartPC(cx, frameIter, spindex, skipStackHits, v, &valuepc))
         return false;
     if (!valuepc)
diff --git a/js/src/vm/Stack.cpp b/js/src/vm/Stack.cpp
index a9c585b295..cdc1046bcc 100644
--- a/js/src/vm/Stack.cpp
+++ b/js/src/vm/Stack.cpp
@@ -1331,6 +1331,21 @@ NonBuiltinScriptFrameIter::settle()
     }
 }
 
+bool
+ FrameIter::inPrologue() const {
+  if (pc() < script()->main()) {
+    return true;
+  }
+  // If we do a VM call before pushing locals in baseline, the stack frame will
+  // not include space for those locals.
+  if (pc() == script()->code() && isBaseline() &&
+      data_.jitFrames_.baselineFrameNumValueSlots() < script()->nfixed()) {
+    return true;
+  }
+
+  return false;
+}
+
 ActivationEntryMonitor::ActivationEntryMonitor(JSContext* cx)
   : cx_(cx), entryMonitor_(cx->runtime()->entryMonitor)
 {
diff --git a/js/src/vm/Stack.h b/js/src/vm/Stack.h
index 6b1b5ba993..b0d29831a3 100644
--- a/js/src/vm/Stack.h
+++ b/js/src/vm/Stack.h
@@ -1884,6 +1884,9 @@ class FrameIter
 
     // This is used to provide a raw interface for debugging.
     void* rawFramePtr() const;
+    
+    // Determines if we're in the prologue of a baseline function.
+    bool inPrologue() const;
 
   private:
     Data data_;